Primary malignant pericardial mesothelioma (PMPM) is a rare pericardial malignant tumor. Most of the manifestations are localized or diffuse masses surrounding the heart. Because of the difficulty of surgical resection, the prognosis of diffuse PMPM is poor, while the edge of localized PMPM is clear and easy to be resected, but it is difficult in diagnosis Timely diagnosis and proper treatment are the key to a good prognosis. Here, we report a patient with localized PMPM and describe the diagnostic method for the diagnosis of the disease.